My husband has just posted on FB regarding this incident. I won't cut and paste directly but - there are a lot of calls citing firearms as a factor. The protocol would normally state that only armed police should respond. However, there are not enough. So they have to do a kind of risk analysis and determine whether it is indeed a real thread of an armed incident or one of the (many) mistakes or hoaxes. If the latter, unarmed police (such as my DH) will attend.
He has attended many which he ought not to have done. One one occasion, he had to beg to be allowed to take riot squad officers with him to arrest a man known to be dangerous. His Sgt made it very clear he thought DH rather cowardly, not going on his own, but in the end conceded, and a team went with him,
It is good they did, since there was an acid attack (on the news at the time) and 17 officers ended up in hospital. If DH had gone alone, the very best outcome would have been total blindness and years of facial reconstruction surgery.
Of course, effective funding if police posts will not guarantee total safety for all. but make no mistake: this event could be prevented if the police were adequately funded, and had not lost 6,800 posts since the Tories came to power.